Optical transmission systems are being increasingly used for data transmission and transmission of TV and radio channels. In general, such an optical transmission system includes an optical fiber, a semiconductor laser used as a light generator, and a light detector. The semiconductor laser emits light with a certain characteristic wavelength. This characteristic wavelength is basically dependent on the material used, but can be set within a certain wavelength range by the effect of heat, for example. In order to increase the amount of data that can be transmitted by an optical fiber, a plurality of semiconductor lasers associated with one optical fiber and operating at different wavelengths can be used. In this case, however, the wavelengths should be strictly observed, so that the data can be clearly differentiated at the end of the transmission.
The characteristic wavelength of semiconductor lasers varies within a tolerance range determined by the manufacturing technology; therefore, semiconductor lasers must be tuned prior to data transmission. For this purpose, devices known as resistance heaters are used, which change the characteristic wavelength of a semiconductor laser using a conductor mounted on a substrate by a thermal effect. Tuning is generally performed by setting the voltage applied to the electric conductor of the resistance heater, a voltage source being assigned in this case to each resistance heater.
A disadvantage of this method, however, is that it requires a very complex design. Furthermore, the arrangement cannot be tuned in a simple manner at a later time.